1. Field of the Invention
The present invention relates to a laboratory jack with improved stability over a larger range of motion.
2. Description of the Background of the Invention
There are many devices designed for lifting and/or lowering objects in a controlled manner. Usually called lifts or jacks, such devices span a wide range of applications from lifting very heavy objects, such as automobiles, to the controlled lifting and placement of very small objects. There is also a wide range of basic designs for such jacks. For example, some jacks have a vertical actuator that moves a load platform directly up and down by means of a linear actuator, e.g., a hydraulic piston or a vertically oriented worm drive having a threaded rod that is connected directly to the platform to move it up and down.
Another common type of jack is a scissors jack. Generally a scissors jack includes a base and a lifting platform that are interconnected by a number of lift links or scissor arms connected in a crossing pattern and a drive actuator that is oriented transverse to the direction of lift, i.e., horizontally. The drive actuator moves the ends of the scissor arms toward or away from each other so as to cause the scissor arms to pivot about each other at a pivotable connection point thereby moving the lifting platform upwardly and downwardly. In its most basic state, and as the term will be used variously throughout this application, a scissor assembly has two scissor arms that cross each other and are connected by a pivot located at a central region of both scissor arms, such as a pin extending through both scissor arms. The upper ends of the scissor arms move up or down from a fixed base that supports the lower ends of the scissor arms depending on the rotation of the arms with respect to each other. A scissors jack assembly as used herein includes one or more such scissor assemblies.
One specific application for which lifts are often used is in a laboratory. So called laboratory jacks are often used to position relatively small objects supported thereon at a selected position at a relatively high accuracy. FIG. 1 shows a typical prior art laboratory jack that is a scissors-type jack.
The laboratory jack has a bottom plate for resting on a support surface, such as a table, and a top plate for supporting an item to be moved up and/or down. Interconnecting the top plate and the bottom plate is a dual column, two-tiered scissors-type lift assembly. The lift assembly has a left side column and a right side column, which are substantially identical to each other and are interconnected by cross-bracing members such that the left side column and the right side column move in parallel tandem at all times.
Each column has two levels or tiers, an upper scissor assembly and a lower scissors assembly, wherein each scissor assembly is made of two scissor arms, such as elongated rigid links, that are pivotally connected to each other at the centers thereof. The lower ends of the scissor arms of each upper scissor assembly are pivotally connected to the upper ends of the scissor arms of the lower scissors assembly, whereby when one scissor assembly is pivoted, it causes the other scissor assembly to pivot in the same manner. The lower end of one of the scissor arms in each lower scissor assembly is pivotally connected in a fixed position to the bottom plate, and the lower end of the other scissor arm of each lower scissor assembly is free to slide laterally across the bottom plate toward and away from the fixed connection. Similarly, the upper end of one of the scissor arms of each upper scissor assembly is pivotally mounted in a fixed position to the underside of the top plate, and the upper end of the other scissor arm of each upper scissor assembly is free to slide toward and away from the fixed connection along the underside of the top plate.
The lower end of the laterally shiftable scissor arm of each lower scissor assembly is slidably connected to a guide track formed of a vertical rail having an elongated slot therein by a pin or wheel that slides along the slot. The slot limits the lateral movement or travel distance of the laterally shiftable scissor arm and also holds the lower end of such scissor arm in lateral alignment with the fixed lower end of the other scissor arm.
Each connection of the upper and lower ends of the scissor arms and left and right side columns is substantially identical thereto, which thereby maintains all of the scissor arms of each respective column in a single plain of motion. The left side column and the right side column are linked by a number of cross-bracing members, such as rods or bars. For example, the left and right lower shiftable ends of the lower scissor assemblies are connected by a first rod, the respective left and right lower fixed pivotable ends of the lower scissor assemblies are interconnected by a second rod, and the central pivot points of the lower scissor assemblies are connected by yet another rod.
The laboratory jack is actuated up and down by a threaded rod oriented substantially perpendicular to the direction of motion of the top plate and bottom plate, i.e. horizontally where the top plate moves vertically. The threaded rod is connected to and extends through two opposing rod mount blocks, which connect the lower ends of the upper scissor arms with the upper ends of the lower scissor arms. The threaded rod has a threaded connection with at least one of the rod mount blocks. When the threaded rod is twisted in a first direction, the rod threads urge the two rod mount blocks together, which causes each of the upper scissor assemblies and lower scissor assemblies to pivot about their respective central pivot points thereby extending the scissors-type jack assembly vertically upwardly and moving the top plate up. Twisting the threaded rod drive in the opposite direction then allows the reverse action to occur, thereby moving the top plate downwardly.
Although the prior art laboratory jacks as described herein are sufficient to move an object up and down in a controlled manner, these laboratory jacks are often limited by a combination of the distance of travel available, the amount of weight that can be supported, and the overall stability of the laboratory jack under larger weight and larger travel distances. The inventor of the present application has sought to provide a laboratory jack that can be used for high tolerance applications and that can provide increased stability for larger weights over longer travel distances.